For many years it has been known that exposure of child or adult teeth to the fluoride ion provides resistance to later decay. A number of methods of furnishing fluoride ion to teeth exist.
Fluorides have been found effective when ingested. This fact has led to the wide scale fluoridation of public water supplies. In fluoridation sodium fluoride or fluorosilic acid is commonly used. The concentration of fluoride ion in public water is generally limited to one part per million. In areas where fluoridated public water is unavailable sodium fluoride solution is available by prescription.
In addition to direct ingestion, topical exposure of developing, existing, and mature teeth to fluoride has been used. There have been continuing efforts to include fluoride in toothpaste. A major problem with such formulations is the incompatibility of the fluoride with abrasives (commonly some form of silicon dioxide). Sodium fluoride is usually used as the source of fluoride ion. If the media is acidic i.e. pH&lt;7 the fluoride ion will bond to silica removing it from availability to the teeth.
Stannous fluoride is sometimes used as a source of fluoride. This is due to the discovery that the stannous ion reacts with the naturally occurring phosphate in the teeth to form highly decay resistant stannous fluorophosphate.
Various fluoride rinses and gels have also been tried. The simplest method has been exposing the teeth in situ to a solution containing the fluoride ion. Such rinses commonly include water containing sodium fluoride, a flavoring agent, and a dye. The more effective stannous fluoride is not used because it is unstable in combination with water. The flavoring agent makes the solution palatable and the dye serves to distinguish the solution from water. This method has several disadvantages. First, the exposure of teeth to the non-viscous solution is brief in the most common use. Second the water solution cannot be pushed into the sulcus of the tooth where root caries develop. Third, such solutions cannot be brushed where brushing opens more sites on the teeth for bonding. This is because brushing agitates the tooth surface sweeping away microscopic debris. These factors reduce the effectiveness of rinses. As a consequence gels have beer designed which solve some of these problems but present other problems.
As an alternative to gels and rinses, foams have been proposed for use as a carrier of fluoride. The only one of these preparations to have found any commercial success is that proposed in U.S. Pat. No. 4,770,634 to Michael Pellico (Pellico). In Pellico there was provided a foamable fluoride composition comprising a water soluble dental fluoride in an amount to provide the composition with about 0.5 to about 5 wt % available fluoride; and an orally compatible and acid stable foaming agent in an amount from about 4 to about 20 wt %; and an orally compatible and acid stable foam-wall thickener in an amount from about 2 to about 20 wt. %; and an orally compatible acidifying agent in an amount to provide the composition with a pH from about 3.0 to about 4.5; and water to 100 wt %.
In accordance with Pellico there is provided a method for treating teeth with a fluoride foam which comprises: dispensing a pressurized and foamable fluoride composition from an aerosol container into the trough of a dental tray to form a fluoride foam within the trough, wherein the foamable fluoride composition has the above composition. The process is then completed by superimposing the trough of the dental tray and its fluoride foam content about and into engagement with the teeth to effect fluoride uptake by said teeth.
Attendants with the advantages of aerosol foam are disadvantages related to the use of aerosols. In addition to above components one must use a pressure container and a propellant in order to create the foam. Pressure containers are more expensive than non-pressurized containers and have higher manufacturing costs. Pressure containers can only be cylindrical, drastically limiting the choice of container shape. Aerosol containers by their very nature cannot be completely emptied or refilled, increasing waste. In addition, the propellant may be incompatible with some compositions. Chlorofluorocarbons are banned from use due to their ozone depletion effect. Some of the replacements proposed such as propane are flammable and others such as nitrous oxide may have physiological effects. Accordingly, there is a commercial need for a fluoride foam that is nonflowable and which requires substantially less fluoride in the tray to achieve the same fluoride uptake as a corresponding volume of fluoride gel without the disadvantages of aerosol foams.
Non-aerosol foamers have been tried to accomplish the above goals. One such foamer is described in U.S. Pat. No. 5,665,332. In all such foamers a problem arose due to the interaction of the fluoride ion, with the container, and foamer. The foams work well at first but lose favorable characteristics on storage. On several occasions noxious gases have been detected in the container. These problems have stopped the widespread adoption of non-aerosol foamers.
In order to dispense non-aerosol foam a special pump-valve or foamer is used. Such a valve commonly mixes air with a composition containing a foaming agent and an active ingredient such as sodium fluoride or hydrofluoric acid each time the activator is depressed. Unfortunately, the fluorides present react with many of the materials present in foamers especially in combination with air. The major problem that has arisen is that the foamer pump piston sticks in the downward position upon standing. Accordingly to date there has not been a commercially successful non-aerosol fluoride foam.